Described herein are toner and developer compositions that include additives comprised of styrene homopolymer or copolymers, among other conventionally sized external additives, on external surfaces of the toner particles.
U.S. Pat. No. 5,763,132, incorporated herein by reference in its entirety, describes a process for decreasing toner adhesion and decreasing toner cohesion. The process comprises adding a hard spacer component of a polymer of polymethyl methacrylate (PMMA), a metal, a metal oxide, a metal carbide, or a metal nitride, to the surface of a toner comprised of resin, wax, compatibilizer, and colorant excluding black. The toner surface additives are blended with the toner, and the hard spacer component is permanently attached to the toner surface by injection in a fluid bed milling device during the size reduction process of the toner. See the Abstract and column 1, lines 9-28.
U.S. Pat. No. 5,716,752, incorporated herein by reference in its entirety, also describes a process for decreasing toner adhesion and decreasing toner cohesion. The process comprises adding a component of magnetite, a metal, a metal oxide, a metal carbide, or a metal nitride to the surface of a toner comprised of resin, wax, and colorant by blending. The component is permanently attached to the toner surface by injection in a fluid bed milling device during the size reduction process of the toner. See the Abstract.
U.S. Publication No. 2004/0137352, incorporated herein by reference in its entirety, describes a toner composition including toner particles having at least one spacer of latex particles or polymer particles attached to the toner particles, in which the latex or polymer particles have an average particle size of from about 60 nm to about 500 nm. The spacer includes latex particles of rubber, acrylic, polyacrylic, fluoride or polyester latexes and/or polymer particles of polymethyl methacrylate, polyvinylidene fluoride, melamine or polytetrafluoroethylene.
Toner particles including larger size silica particles, for example sol-gel silica particles having a size of from about 100 to about 150 nm, on external surfaces thereof have also been used. Sol-gel silicas are silicas synthesized by the controlled hydrolysis and condensation of tetraethoxysilane. The sol-gel process is typically carried out in alcohol solvents with added homopolymer solutes to control the structure of the precipitated silicon dioxide product. Examples of alcohol solvents used in the sol-gel process include methanol, ethanol and butanol. Such silica particles achieve toner charge stability and reduce impaction into the toner particles of smaller sized metal oxide surface additives such as silica and titania. See, for example, U.S. Pat. No. 6,610,452, incorporated herein by reference in its entirety. While these sol-gel silicas perform adequately, including in terms of relative humidity (RH) sensitivity, they are relatively expensive.
What is still desired is a less expensive external additive alternative to sol-gel silicas, and preferably offering the same or improved performance as sol-gel silica external additives.